This invention relates to throttle valve control devices which control the throttle valve of an automotive engine by means of an actuator such as a DC or stepping motor.
Conventionally, the throttle valve of an automotive engine has been mechanically coupled to the acceleration pedal of the automobile. However, for the purpose of improving the operator's driving feeling or providing a constant speed cruising function, the so-called drive-by-wire method has already been proposed and has widely been adopted, by which the throttle valve is driven by an actuator such as a DC or stepping motor. In such throttle valve control devices, the degree of opening of the throttle valve is adjusted by an actuator in response to the outputs of the acceleration pedal kick-in sensor and the speed sensor.
FIG. 1 shows an overall organization of such a throttle valve control device for an automotive engine including an actuator for driving the throttle valve; this device is similar to those disclosed, for example, in Japanese Patent Publication No. 43-1687 and Japanese Laid-Open Patent Application No. 57-76236. As shown in the figure, the supply of a mixture of air and fuel to an internal combustion engine 1 via the air intake pipe 2 is controlled by a throttle valve 3; the valve 3, which rotates on the shaft 3a, is urged by a return spring 4 to the position at which it closes the air intake pipe 2 completely. The shaft 3a of the throttle valve 3 is coupled, via an electromagnetic clutch 5, to the actuator 6 such as a DC motor or stepping motor. The output shaft of the clutch 5 is coupled to the shaft 3a of the throttle valve 3, while the input shaft thereof is coupled to the actuator 6; thus, the electromagnetic clutch 5 connects and disconnects the actuator to and from the shaft 3a of the valve 3a by means of the friction plates coupled to the input and output shafts thereof.
The actuator 6 and the clutch 5 are driven and controlled by a control means 7, which consists, for example, of a microprocessor. The portion 7a for controlling the actuator 6 comprises an actuator controller 71; on the other hand, the portion 7b for controlling the clutch 5 comprises a failure detector 72 and a clutch driver circuit 73. The actuator controller 71 controls the actuator 6 to adjust the opening of the throttle valve 3; namely, the actuator controller 71 controls the opening of the valve 3 via the actuator 6 so that the opening of the valve 3 is adjusted in accordance with a function of the following two variables: the amount of kick-in of the acceleration pedal by the operator of the automobile, which is detected by the acceleration pedal kick-in sensor 8 coupled to the acceleration pedal 9, and the speed of the automobile detected by the speed sensor 10. The degree of opening of the throttle valve 3 is usually adjusted in such a manner that a good driving feeling is provided for the operator of the automobile; in the constant speed cruising mode of the automobile, on the other hand, it is set at a level at which the automobile will cruise at the target speed that is detected from the amount of kick-in of the acceleration pedal 9. Thus, in the case of the above device shown in FIG. 1, the opening of the throttle valve 3 is not directly controlled by the acceleration pedal 9; it is controlled via the actuator 6 on the basis of an arbitrarily selected function of the amount of acceleration pedal kick-in, with an automobile speed feedback via the speed sensor 10.
The clutch driver circuit 73, on the other hand, disconnects the clutch 5 when the failure detector 72 detects a failure. Namely, when the acceleration pedal sensor 8 or the actuator 6 fails, the output power of the engine 1 may thereby be increased against the intention of the operator of the automobile; thus, the failure detector 72 detects, for example, occurrences such as: the case where the output of the acceleration pedal sensor 8 is outside of a predetermined range; the case where the actuator 6 becomes incapable of proper operation due to the disconnection in the electrical circuits thereof; or the case where the driving circuit of the actuator 6 fails. In response to the output signal of the failure detector 72, the clutch driver circuit 73 stops the supply of the driving current to the electromagnetic clutch 5 to disconnect the throttle valve 3 from the actuator 6; the throttle valve 3 is thereby urged by the return spring 4 to close the air intake pipe 2.
The above failure detection system, however, has the following disadvantage. Namely, it is difficult to detect the failures as described above with complete certainty. In particular, in the case where the failure detector circuit 72 itself fails simultaneously with other circuits, or where the clutch drive circuit 73 fails, the clutch driver 73 may continue to supply the driving current to the electromagnetic clutch 5 in spite of such failures. Then, the revolutions per minute of the engine may be abnormally increased against the intention of the operator of the automobile. In the worst case, the operator may lose control over the automobile which begins to run away against his or her will.